Just because it isnt possible now with out current level of technology doesnt mean it isnt possible.
There is something between isolated particle theory and gravitational drives here that applies...but that is instinctual...I am no scientist.
I firmly think the key to faster that light travel is unlocking the mystery of gravity's effect on local space time.
The energy required to break away from local space time and the gravity well must be enormous.
Dare I say it....God like.
If anybody is out there doing that it must not leave a trace. That we’ve thought to look for. But tremendous energy expenditures should leave some kind of signature.
At any rate they will still have to wait 20k light years to get our messages before they can employ their instantaneous star travel tech.